Utilising confinement reinforcement for shear resistance in reinforced concrete structures

Common transverse reinforcement of reinforced concrete members with circular cross-section consists of round ties or spirals. Its purpose in members that are not subjected to significant shear loading is to provide proper confinement for concrete, and eliminate buckling of the longitudinal reinforcement bars. If spirals are to be used as both shear enabler and confiner for reinforced concrete beams then, under combined action of moment and shear, spirals will be required to provide or contribute to proper shear resistance. Hence, a proper assessment for spiral shear contribution is required. The validity of concepts which underline current methods for shear design used in design codes will be investigated in this paper, especially for beams with the shear configuration, which violates basic code rules on forming a truss. A simplified sectional model based on sectional crack analysis and a corresponding approach in assessing the shear contribution of spiral shear reinforcement are presented. A method for evaluating the shear capacity of beams with spirals has also been proposed

Impact of Joint Modeling Approach on Performance Estimates of Older-Type RC Buildings

The behavior of beam-column connections has usually been ignored in the modeling process due to its complexity and relatively recent awareness of its possible impact on response. This study presents the features of modeling unrein-forced beam-column joints in estimating seismic demands. A representative RC frame is subjected to strong ground motions. Through nonlinear dynamic analyses, base shear, roof displacement, inter-story drift and joint rotation are noted. The dynamic analyses are performed comparatively through two analytical models with rigid and flexible joint assumptions. In the flexible joint model, shear deformation at the beam-column joint and bond-slip deformation at the beam-column interface are simulated through a previously verified analytical representation. Results indicate that introducing unreinforced beam-column joint behavior to the model may lead to almost two times larger seismic demands compared to those obtained from rigid connection assumption. Thus, the performance assessment of such buildings may conclude erroneously with underestimated seismic demands and damage levels when inelastic actions in the joints are ignored. However, in some cases, lower seismic demands can also be obtained for the flexible joint model